The present application is the U.S. national stage application of International Application PCT/EP00/06143, filed Jun. 30, 2000, which international application was published on Jan. 11, 2001 as International Publication WO 01-2186 in the French language. The International Application claims priority of Luxembourg Patent Application 90412, filed Jul. 2, 1999.
Numerous packaging material coating processes are known, the following being a non-exhaustive list:
aqueous coating in which the liquid to be coated is a suspension or solution of an agent in water;
solvent coating in which the liquid to be coated is a suspension or solution of an agent in one or more solvents;
hot-melt coating in which the liquid to be coated is obtained by adjusting the agent to be deposited to a temperature which makes it liquid;
solvent-free coating in which the agents to be deposited are in liquid form (monomers) and will cure and polymerise by catalysis;
coating by evaporation of a solid which sublimes under vacuum onto the support;
lamination coating in which the coating is a film which is attached to the support with an adhesive;
transfer coating in which the agent to be deposited is already provisionally attached to a film to which it adheres poorly in order to be removed from the provisional support and finally attached to the final support by some known means.
The coating provided by these processes is generally complete, sometimes partial, but none of these coating methods allows the production of high resolution patterns.
U.S. Pat. No. 5,721,007 describes a process in which a support is coated with a metallic layer; an electrically insulating lacquer is printed at high resolution onto a first part of the coated support; one or more metallic layers are deposited onto a second part of said support, i.e. the part of the support not covered by the lacquer, by electrolysis in order to form the conductive tracks of the circuit; the electrically insulating mask is then removed in order to allow engraving of the support coating not covered by said metallic layer or layers deposited onto said support between the lacquer. This method is used, for example, in the production of electrical circuits, in particular for the production of flat cables. Although this method allows high resolution printing, it does not permit deposition of metal onto the lacquer.
The object of the present invention is accordingly to provide a process for the production of a multilayer substrate having high resolution patterns and permitting deposition of metal onto the lacquer.
This object is achieved according to the invention by a process allowing the production of high resolution patterns and comprising the following steps:
high resolution printing of a lacquer on the coated support;
treatment of the support by electrolysis;
washing and drying of the support.
According to an important feature of the invention, the lacquer is a charged lacquer. Said charged lacquer not only allows specific areas on the support to be protected, but also allows subsequent deposition of metal onto said charged lacquer.
High resolution printing of a lacquer onto a support allows the creation of fine and high resolution patterns on this support. This process is independent of the support and the support coating process. This process may, in principle, be applied to any support.
Before printing, the support may be coated with a layer which preferably comprises metal.
Said charged lacquer which may for example comprise conductive materials and/or materials acting as a barrier to or filtering electromagnetic waves.
The material acting as a barrier to or filtering electromagnetic waves preferably absorbs and/or reflects at least part of the electromagnetic waves.
Treatment of the coated support by electrolysis advantageously comprises electrolytic engraving of the coating on the unprinted part of the coated support.
According to one specific embodiment, said support is subjected to electrolytic deposition on the conductive printed part after washing and drying.
Treatment of said support by electrolysis comprises electrolytic deposition of one or more metals or the alloys thereof onto the printed part of the support.
The lacquer is preferably printed onto said support by photogravure. Photogravure is advantageously performed by a photogravure unit comprising at least one cylinder having printing zones consisting of engraved cells, the outermost cells of each pattern being interconnected to ensure linear continuity of the outlines. The cylinder cells are preferably arranged at a screen ruling of 175 to 700 cells per inch (per 2.5 cm), preferably of 350 cells per inch (per 2.5 cm). The cells of the outlines are preferably interconnected to achieve continuity of the graphical element and avoid any stepped appearance. Said photogravure unit is capable of printing a coating with very fine patterns of between 150 and 25 xcexcm, preferably of 50 xcexcm.
Engraving is preferably performed by electrolysis between the metallic coating of the support to be treated and an anode immersed in an aqueous electrolyte. Said anode is preferably a titanium anode consisting of folded sheet. Said aqueous electrolyte advantageously comprises an inorganic acid and the salt thereof or an inorganic base and the salt thereof, preferably NaOH+NaCl at a concentration of 10%. Once the lacquer has been applied onto the coated support, the electrolytic treatment of the support allows the removal of the coating from said support at those points where the lacquer was not applied. In this manner, a support comprising high resolution patterns is obtained. The electrolyte is selected such that the products released into the aqueous phase by electrolysis attack the metallic coating with a mixture of the acidic type and the salts thereof or alternatively with an alkali and the halogen salts thereof. Depending upon the electrolyte selected and the density of the printed pattern, products are obtained which have different characteristics with regard to reflection, transmission and absorption of incident electromagnetic radiation. Reflection and transmission rates may preferably range between 0 and 100%, while the absorption rate may range from 0 to 50%.
Electrolytic deposition is preferably performed by electrolysis of one or more metals and/or the alloy thereof, by dissolution of a soluble electrode containing at least the electrode metal or metals. The metallic deposit or successive metallic deposits allow(s) the creation of patterns with high resolution and high precision on a support.
The products of the process described above may have useful properties, especially for applications in the field of electromagnetic waves, in particular in the field of microwaves.
The process allows the production of multilayer products having very particular properties with regard to the reflection, transmission and absorption of incident electromagnetic radiation. Depending upon the particular case, incident electromagnetic radiation on the product maybe transmitted at a rate of 0 to 100%, reflected at a rate of 0 to 100% and/or absorbed at a rate of 0 to 50%. Such products have many and varied applications; they may be used, for example, as a filter for electromagnetic radiation, said filters being transparent to visible light. A heat-resistant polymeric film, for example of polyester, may be coated with a layer which heats up when the incident electromagnetic energy is partially absorbed by the coating. Said coating may be metallic with a resistivity of between 0.0005 and 0.1 ohm/square, preferably of 0.01 ohm/square, for example of aluminium with a thickness of between 0.001 and 1 xcexcm. Under these conditions, the product is visually highly transparent and heats up to elevated temperatures (of the order of 200 to 300xc2x0 C.) when struck by electromagnetic radiation and in particular by microwaves. The calorific energy may amount to up to 50% of the incident energy.
The quantity of energy which is absorbed, transmitted or reflected varies as a function of the dimensions and distribution of the coating applied to the film. Below a predetermined threshold, the transmitted energy is greater than the reflected energy; beyond this threshold, transmitted energy is less than the reflected energy.
By filling the lacquer with agents which enhance the electromagnetic wave absorption effect, it is possible to create products which are opaque to electromagnetic waves. In this way, it is for example possible to create film which is opaque to microwaves which could be applied to the window of a microwave oven door. By providing a grid with thin lines at a spacing of half the wavelength of the microwaves, a microwave barrier film is obtained which is almost completely transparent to visible light waves. Said film may be applied onto a microwave oven door, through which the interior of the microwave oven may readily be observed in complete safety.
The process also allows the creation of multilayer products. A second metallic deposit may be deposited onto a first metallic deposit by passing the support again through the printing station and the treatment station. Of course, the number of times the support passes through the printing and treatment stations and, consequently, the number of metallic deposits, is not limited to two.
Depending upon the nature of the coating and the filler in the applied lacquers, it is possible to create products, the composition of which is determined by the desired electromagnetic energy conversions. It is also possible to create barriers to electromagnetic radiation of certain wavelengths. Both options may optionally be combined to provide products which, as a function of wavelength, are both absorbent and reflective.
It is thus possible to create a package which reflects microwaves in one part of the package and absorbs part of the microwaves in another part. This makes it possible to use a microwave oven to heat foods which are to be adjusted to different temperatures.
The present invention also provides a multilayer product comprising the following layers:
base support made from a material transparent to visible light and to electromagnetic waves,
at least one high resolution metallic coating covering less than 5% of the area of the support,
at least one layer of lacquer covering the metallic coating,
in which the coating is arranged on the support in a pattern invisible to the naked eye, filtering a specific range of electromagnetic waves.
For the purposes of the present document, the term xe2x80x9cfilteringxe2x80x9d means that between 0 and 99.9% and preferably between 0 and 95% of the incident waves pass through the product. The product may thus be virtually transparent or opaque to a specific range of electromagnetic wavelengths.
For the purposes of the present document, the term xe2x80x9ctransparent to visible lightxe2x80x9d means that between 80 and 99.9% and preferably between 90 and 95% of visible light pass through the product.
According to an advantageous embodiment, the product comprises an additional metallic coating layer which covers at least part of the lacquer layer.
According to another embodiment, the invention relates to a multilayer product comprising the following layers:
base support made from a material transparent to visible light and to electromagnetic waves,
high resolution lacquer covering at least 5% of the area of the support,
at least one metallic coating covering the lacquer and filtering a specific range of electromagnetic waves,
in product the lacquer is arranged on the support in a pattern invisible to the naked eye.
An additional lacquer layer may, at least in part, cover the metallic coating which may in turn be covered, at least in part, by an additional coating layer.
The base support is generally a film of a synthetic material, such as for example a polyester film. However, any other material may be suitable provided that it is transparent to visible light and to the selected range of electromagnetic waves. It is moreover necessary for it to be possible to cover such a material with a high resolution pattern comprising a coating and/or a lacquer.
The proposed product generally absorbs between 0 and 95% of the specific range of incident electromagnetic waves, reflects between 0 and 100% and/or transmits between 0 and 100% of the non-absorbed waves as a function of the pattern, the nature and quantity of the coating.
According to a particular embodiment, the product absorbs from 0 to 50% of the energy of the electromagnetic waves and reflects and/or transmits the non-absorbed energy.
The product thus comprises a filter for a range of electromagnetic waves and transparent to visible light; it may even comprise a filter which is opaque to electromagnetic waves and transparent to visible light.
In particular, the electromagnetic waves are, for example, microwaves and the product may consequently be used as packaging for microwaveable products, i.e. for packaging foodstuffs which may be reheated in a microwave oven.